The Defenders will also certainly be cancelled because its ratings are terrible.

Once this season’s initial ratings results were in, there was/is absolutely no chance either show would make it to the 2011-12 season.

Why didn’t CBS just give Medium a full order for the rest of the season and yank The Defenders off the schedule in mid-season?

Impossible to know for certain. Perhaps CBS still thought The Defenders had a chance when they extended its original 13 episode order. Perhaps CBS wanted to score the PR points by extending the orders of all their freshmen series. Perhaps when choosing which low rated show they wanted to use in the Friday 8pm hour in the spring, the episode cost of The Defenders was more attractive.

Whatever the reason, Medium’s fate was sealed by its own dreadful ratings, CBS didn’t expect to increase its ratings on Friday at 8pm by substituting The Defenders. It was making the best of a bad situation between two poorly rated shows.